FIG. 1 illustrates an exemplary structure of a general E-UTRAN (Evolved Universal Terrestrial Radio Access Network) system according to the related art and the present invention.
The E-UTRAN system as shown in FIG. 1 has been evolved from the conventional UTRAN system and a third generation partnership project (3GPP) currently proceeds with basic standardization operations. The E-UTRAN system is also called an LTE (Long Term Evolution) system.
The E-UTRAN system includes base stations (eNode Bs or eNBs) 21 to 23, and the eNBs 21 to 23 are connected via an X2 interface. The eNBs 21 to 23 are connected with a terminal (or user equipment (UE)) 10 via a radio interface and connected to an EPC (Evolved Packet Core) 30 via an S1 interface.
Layers of a radio interface protocol between the terminal 100 and a network may be divided into a first layer L1, a second layer L2, and a third layer L3 based on the three lower layers of an open system interconnection (OSI) standard model which is widely known in communication systems. A physical layer belonging to the first layer among the three lower layers provides an information transfer service using a physical channel, and a radio resource control (RRC) layer positioned at the third layer serves to control radio resources between the UE and the network. For this, the RRC layer exchanges an RRC message between the UE and the network.
FIG. 2 illustrates the structure of a radio interface protocol between the UE and a UTRAN (UMTS Terrestrial Radio Access Network) according to the 3GPP radio access network (RAN) standards. FIG. 3 is an exemplary view of a physical channel.
The radio interface protocol as shown in FIG. 2 has vertical layers comprising a physical layer, a data link layer, and a network layer. The radio interface protocol has horizontal planes comprising a user plane (U-plane) for transmitting data information and a control plane (C-plane) for transferring control signaling.
The protocol layers in FIG. 2 may be divided into a first layer L1, a second layer L2, and a third layer L3 based on the three lower layers of the open system interconnection (OSI) standard model which is widely known in communication systems.
The physical layer, namely, the first layer L1, provides information transfer service to an upper layer by using a physical channel. The physical layer is connected to an upper layer called a medium access control (MAC) layer via a transport channel. The physical layer transfers data to the MAC layer via the transport channel.
Data is transferred via the physical channel between different physical layers, namely, between a physical layer of a transmitting side and that of a receiving side. The physical channel is demodulated according to an OFDM (Orthogonal Frequency Division Multiplexing) method, and utilizes time and frequency as radio resources.
The second layer L2 is divided into two lower layers. Namely, the second layer is divided into a MAC layer and an RLC layer. The MAC layer provides a service to the RLC layer, the upper layer of the MAC layer, via a logical channel. The RLC layer supports data transmission with reliability. Here, the function of the RLC layer may be implemented as a function block within the MAC layer. In such a case, the RLC layer may not exist.
Although not shown, the second layer further comprises a PDCP layer. The PDCP layer performs a function called header compression that reduces the size of a header of an IP packet, which is relatively large and includes unnecessary control information, in order to effectively transmit the IP packet such as an IPv4 or IPv6 through a radio interface with a narrow bandwidth.
The RRC layer corresponding to the third layer is defined only in the control plane, and controls a logical channel, a transport channel and a physical channel in relation to configuration, reconfiguration, and the release of radio bearers (RBs). In this case, the RBs refer to a service provided by the second layer for data transmission between the UE 10 and the UTRAN. When an RRC connection is established between the RRC layer of the UE 10 and that of the radio network, the UE 100 is defined to be in an RRC connected mode, or otherwise, the UE 100 is defined to be in an idle mode.
A NAS (Non-Access Stratum) layer exists at an upper position of the RRC layer. The NAS layer performs a function of session management, mobility management, etc.
The physical channel, the transport channel, and the logical channel will now be described in more detail.
First, each cell formed by each of the eNBs 21 to 23 is set with one of bandwidths 1.25 Mhz, 2.5 Mhz, 5 Mhz, 10 Mhz, 20 Mhz, etc., and provides downlink or uplink physical channels to several terminals. In this case, each different cell may be set to provide each different bandwidth.
As noted with reference to FIG. 3, the physical channel comprises several sub-frames of a time axis and several sub-carriers of a frequency axis. Here, a single sub-frame comprises a plurality of symbols at the time axis. A single sub-frame comprises a plurality of resource blocks, and a single resource block comprises a plurality of symbols and a plurality of sub-carriers. Each sub-frame may use particular sub-carriers of particular symbols (e.g., a first symbol) of a corresponding sub-frame for a PDCCH (Physical Downlink Control Channel), namely, an L1/L2 control channel. A single sub-frame is 0.5 ms, and a TTI (Transmission Time Interval), a time unit for data transmission, is 1 ms corresponding to two sub-frames.
Next, the transport channel includes a downlink transport channel for transmitting data from a network to a terminal and an uplink transport channel for transmitting data from the terminal to the network. The downlink transport channel for transmitting data from the network to the terminal includes a broadcast channel (BCH) for transmitting system information, a paging channel (PCH) for transmitting a paging message, and a downlink shared channel (DL-SCH) for transmitting user traffic or a control message. The downlink traffic of a broadcast or multicast service, or the control message of the broadcast or multicast service may be transmitted via the downlink SCH or a separate downlink MCH (Multicast Channel).
The uplink transport channel for transmitting data from the terminal to the network includes a random access channel (RACH) for transmitting an initial control message and an uplink SCH for transmitting other user traffic or a control message.
The logical channel includes a BCCH (Broadcast Control Channel) for broadcasting system control information, a PCCH (Paging Control Channel) for transmitting paging information, a CCCH (Common Control Channel) for transmitting control information between a terminal and a network, or the like. The BCCH is mapped to the BCH of the transport channel, and the PCCH is mapped to the PCH of the transport channel.
The logical channel further includes an MCCH (Multicast Control Channel) for an MBMS (Multimedia Broadcast Multicast Service), an MTCH (Multicast Traffic Channel) for the MBMS service, or the like. The MCCH is used to transmit control information for MBMS transmission to a terminal, and the MTCH is used to transmit the MBMS service to the terminal.
The MBMS refers to providing a streaming or background service to a plurality of terminals by using a downlink-dedicated MBMS bearer service. The MBMS bearer uses a point-to-multipoint radio bearer service and a point-to-point radio bearer service in the UTRAN.
In the above-described related art, the base station periodically transmits control information of the MBMS via the MCCH. However, because the period is so long that the terminal should wait for a considerably long time to receive the control information of the MBMS.